lib/Kconfig: make PRIME_NUMBERS not user selectable.

Linus doesn't like it user selectable, so kill it until
someone needs it for something else.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/lib/Kconfig b/lib/Kconfig
index 1788a1f..f4193a3 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -551,7 +551,7 @@
 	bool
 
 config PRIME_NUMBERS
-	tristate "Prime number generator"
+	tristate
 	default n
 	help
 	  Provides a helper module to generate prime numbers. Useful for writing